U.S. patent number 4,490,731 [Application Number 06/443,410] was granted by the patent office on 1984-12-25 for ink dispenser with "frozen" solid ink.
This patent grant is currently assigned to Hewlett-Packard Company. Invention is credited to John L. Vaught.
United States Patent |
4,490,731 |
Vaught |
December 25, 1984 |
Ink dispenser with "frozen" solid ink
Abstract
A new type of apparatus for dispensing "frozen" solid ink and
the ink for use therein for printing on paper is disclosed. The ink
dye vehicle is chosen to have a melting point above room
temperature, so that the ink which is melted in the apparatus will
not be subject to evaporation or spillage during periods of
non-printing. The vehicle is also chosen to have a low critical
temperature to permit the use of the solid ink in a thermal ink jet
printer.
Inventors: |
Vaught; John L. (Palo Alto,
CA) |
Assignee: |
Hewlett-Packard Company (Palo
Alto, CA)
|
Family
ID: |
23760694 |
Appl.
No.: |
06/443,410 |
Filed: |
November 22, 1982 |
Current U.S.
Class: |
347/88;
106/31.29; 106/31.57; 106/31.58; 219/421; 222/146.5; 346/99;
347/67; 347/99; 392/472; 392/488 |
Current CPC
Class: |
C09D
11/34 (20130101); B41J 2/17593 (20130101) |
Current International
Class: |
B41J
2/175 (20060101); C09D 11/00 (20060101); G01D
015/16 () |
Field of
Search: |
;346/14R,1.1
;219/421,307 ;222/146HE ;239/133,135 ;106/22,31 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Hartary; Joseph W.
Attorney, Agent or Firm: Fromm; Jeffery B.
Claims
I claim:
1. An apparatus for dispensing ink which is a solid at 25.degree.
C. from a reservoir onto a recording media, said apparatus
comprising:
a feed tube having an entrance in contact with the ink in the
reservoir;
a nozzle coupled to the feed tube; and
a resistance heater for melting the ink, said resistance heater
extending from the reservoir through the feed tube to the
nozzle.
2. An apparatus for dispensing ink as in claim 1 wherein the
resistance heater is positioned so as to melt only the solid ink in
the reservoir in immediate proximity with the entrance of the feed
tube.
3. An apparatus for dispensing ink as in claim 1 further
comprising:
a jet resistor in proximity with the nozzle whereby the melted ink
is forced out of the nozzle as a jet of droplets.
4. An apparatus for dispensing ink as in claim 3 wherein electric
current is continuously applied to the ink jet resistor so that the
ink in the nozzle is maintained in a liquid state.
5. An ink for writing on paper with a non-impact printer having
expulsion means for expelling said ink from an orifice, said ink
consisting essentially of:
a dye; and
a vehicle which is a solid at 25.degree. C. consisting of
solvent for said dye, said solvent having a high vapor pressure, a
melting point greater than 25.degree. C., and a critical
temperature less than the degradation temperature of said expulsion
means, and
a binder with a low vapor pressure for binding said dye to said
paper when said solvent has sublimed off of the paper.
6. An ink as in claim 5 wherein said solvent consists essentially
of neopentyl alcohol.
7. An ink as in claim 6 wherein said binder consists essentially of
a varnish soluable in said solvent.
8. An ink as in claim 5 wherein said solvent consists essentially
of difluorotetrachlorenthane.
9. An ink as in claim 8 wherein said binder consists essentially of
a varnish soluable in said solvent.
10. an ink as in claim 5 wherein said binder consists essentially
of a varnish soluable in said solvent.
Description
BACKGROUND OF THE INVENTION
Liquid ink (i.e., a liquid vehicle with dissolved dye pigment) used
in many types of printers is stores in a reservoir and delivered by
a capillary tube to a printing nozzle. In a non-impact printer such
as a liquid ink jet printer, this ink is forced out of the nozzle
in the form of a jet of liquid droplets by heating a resistance
element in close proximity to the nozzle. The ink itself is then
directed at a printing media such as paper to form lines or dots.
The dye is then fixed to the paper by evaporation and
absorption.
Unfortunately, because the ink is a liquid composed of a solvent
used as the transport vehicle for the ink dye, the nozzle tends to
clog due to evaporation of the solvent during periods of
non-printing. Typically, this can happen in a period of less than
five minutes when the solvent chosen is fast drying such as pure
water. Slow drying solvents take longer to evaporate and clog the
nozzle, but at the expense of a long drying time for the print on
the paper. Also, since dyes in evaporative inks are carried by
capillary action into the paper pores during drying, the print
density of such inks is quite limited due to the thin layer of dye
that remains on the paper surface.
Additionally, because the ink is a liquid, there is also the
potential for spillage during handling.
One method of eliminating several of the problems due to the use of
liquid ink is the erosion by means of an electric arc of a solid
ink directly onto the paper as disclosed by Bovio, et al., in U.S.
Pat. No. 4,349,829 issued Sept. 14, 1982. Unfortunately, the Bovio
system requires not only the use of an electrically conductive ink,
but also a high and potentially dangerous electric potential to
move the ink from the reservoir to the paper.
SUMMARY OF THE INVENTION
The present invention solves the problems of the prior art by
utilizing a new and novel "frozen" solid ink which depends on
solidification to fix the dye to the paper. The dye vehicle is
chosen so as to not only be a good solvent for dyes and be low in
toxicity, but also the solvent is chosen so as to be a solid at
room temperature (25.degree. C.). This solid ink can then be melted
by the disclosed apparatus and utilized as a liquid in a manner
similar to many conventional techniques. Because the molten ink
solidifies immediately upon contact with the paper, the dye itself
remains on the paper surface as in offset printing, thus permitting
a greater range of print density and quality.
The preferred embodiment of the solid ink delivery apparatus melts
the ink in a portion of the solid ink reservoir without having to
melt the entire reservoir of ink. In addition a heater is provided
which guarantees that the ink is kept in a liquid state as the ink
is transported to the exist nozzle.
When the thermal ink jetting process is used to eject ink from the
nozzle by means of a jet resistor, in order to prevent undue
thermal stress on the jet resistor it is also necessary to select
the vehicle to have a low critical temperature (i.e., the
temperature at which a liquid will boil independent of the pressure
exerted on the liquid).
DETAILED DESCRIPTION OF THE DRAWING
FIG. 1 shows the apparatus for melting and delivering the solid ink
of the present invention in a thermal ink jet printing system.
DETAILED DESCRIPTION OF THE INVENTION
A new "frozen" solid ink and a delivery system is disclosed for
printing on recording media such as paper. Ink is a dye dissolved
in a solvent which acts as a transport vehicle until the ink dries
or solidifies on the recording media. This vehicle should be a good
solvent for the particular dye chosen and for safety reasons the
vehicle should have low toxicity. In the present invention, the ink
vehicle used is selected so as to be frozen in the solid state at
room temperature (25.degree. C.). The solid ink can then be melted
and used in its liquid state as an ordinary ink. While in the
non-printing mode, the ink is a solid and there is no chance of
spillage. In addition, the vapor pressure of the vehicle while it
is in its solid state should be selected to be low. The low rate of
sublimation of the solid vehicle allows indefinite periods of
non-printing without the danger of nozzle clogging even without
nozzle capping.
In a thermal ink jet printer a further restraint on the choice of
vehicles is required because in such a system the liquid ink is
forced out of the jet nozzle when a jet resistor is heated close to
the critical temperature of the vehicle. Thus, to prevent undue
thermal degradation of the jet resistor, the vehicle should have a
critical temperature below that degradation temperature. For
example, tantalum/aluminum film resistors should not exceed
500.degree. C. Since a passivation layer of 1.0 micron silicon
dioxide having a thermal drop of 100.degree. C. is usually used on
top of such tantalum/aluminum resistors, the vehicle should then
have a critical temperature below 400 degrees C. On the other hand,
if metallic glass resistors are utilized which can withstand much
higher temperatures than tantalum/aluminum film resistors and do
not require a passivation layer, the critical temperature of the
vehicle can be 800.degree. C. to 900.degree. C.
An example of a vehicle suitable for use with either
tantalum/aluminum or metallic glass resistors is a binary
combination of "E" Wax, a derivative of montan wax, available from
the BASF Wyandotte Corp. of Holland, Mich. a subsidiary of BASF Ag,
Federal Republic of Germany, with a melting point (M.P.) of
77.degree. C. to which between 20-70% by volume isopropal alcohol
has been added to reduce the critical temperature below 400.degree.
C. With 50% isopropal alcohol this mixture is a solid with low
vapor pressure up to its 71.degree. C. melting point. A second
suitable vehicle is "V" Wax, which is a polyvinyl ether wax, also
available from the BASF Wyandotte Corp., saturated with 30% by
volume isopropal alcohol. The vehicle may also be a high vapor
pressure, low critical temperature solid such as
2,2-dimethyl-1-propanol (CH.sub.3).sub.3 CCH.sub.2 OH (neopentyl
alcohol) M.P.=52.degree. C., or 2,2- difluorotetrachloroethane
CCl.sub.3 CClF.sub.2, M.P.=41.degree. C. along with appropriate
binders such as a soluable varnish (i.e., alkyd resins) as used in
offset printing to bind the dye or pigment to the paper even if the
vehicle has sublimed off the paper.
In order to deliver this solid ink to the recording media, the ink
dispensing system must be able to melt the ink. In addition, the
creation of the liquid "free surface" to permit the ink to feed
through the associated tubing should be accomplished without have
to melt the entire amount of solid ink as this would require
excessive power and warm-up time.
FIG. 1 shows the apparatus for accomplishing these goals in a
thermal ink jet printing system. The frozen ink 10 is stored in a
reservoir 20. A supply tube 30 connects the reservoir 20 to the
head assembly 40. Inside the head assembly 40 is a small head
reservoir 50 where the jet resistor 60 boils the ink which is then
discharged through the nozzle 70 in the form of a jet of ink
80.
In order to melt the frozen ink 10 and to keep it in a liquid state
85 while printing, a resistance heating wire 90 coupled to a power
supply 100 is passed through the frozen ink 10, through the supply
tube 30, and through the head reservoir 50 and attached to an
electrical common connection 110 in the head assembly 40.
Ordinarily the jet resistor 60 is pulsed with electrical current to
create the ink jet 80. In addition, in the present invention the
jet resistor 60 may be continuously heated by supplying direct
current through the jet resistor 60 or by adding separate heating
resistors to the head (not shown) to insure that the ink is a
liquid when printing is desired.
In order for the supply tube 30 to transport the ink by capillary
action, it is necessary to create a "free surface" 120 of liquid
ink 85 around the tube entrance 130. In general, it is not
necessary to melt the entire reservoir of frozen ink 10; and in
fact to do so would require excess power from the supply 100, as
well as excess warm-up time and the unnecessary added potential for
evaporation of the ink solvent in the reservoir 20. By selecting
the power dissipated in the resistance wire 90, the free surface
120 of liquid ink can be kept to a minimum, and yet still fill the
tube entrance 130 in much the same fashion as liquid wax feeds the
wick of a wax candle.
It would be obvious to one skilled in the art that the present
invention is not limited to thermal ink jet printing and the use of
this invention in other types of printers and plotters can be
accomplished without the inventive faculty. Therefore, the scope of
this invention is limited by the following claims.
* * * * *